Functions have been implemented in various robots to enable them to follow a conversation protocol. The paralinguistic information involved in prosody and posture expression is used to improve the transparency of the conversational states, especially the protocol, thereby effectively contributing to natural and efficient communication. Information is communicated incrementally to enable error handling. Various rules for selecting conversation participants, forming a communication group, and turn-taking are followed. Since all the actions of a conversational robot are explicitly controlled, such robots should be useful for revealing important heretofore unknown conversational functions.